This flag with "the bhoys" is accurate and can be bought from club shops.Stephen Farrell, 17 May 2006

Yet another flag is used by Celtic supporters: a white saltire on a green
background.Thierry Gilabert, 8 May 2004

This image (located by Thierry Gilabert) is
a photo of a flag bearing an IRA slogan, which now appears to be rarely seen.
Celtic Football Club has no association with the IRA.

This flag bears the slogan of the IRA - our day will come. Although this
organisation is unfortunately linked with Celtic, this is not the flag of Celtic
Football Club. In fact that picture must have been taken a long time ago because
the club crest is now copyrighted and such flags cannot be found around Celtic
Park anymore.Stephen Farrell, 17 May 2006

The New York Times today has a piece on the Rangers-Celtic rivalry in Glasgow
and its connection to Protestant-Catholic history. I found it interesting that
Celtic fans wave the flag of the Irish republic at
matches. many Celtic supporters, apparently, are descendants of 19th-century
Irish immigrants. Al Kirsch, 24 April 2011

Many years ago (I think it was in 1961) at a football match where Celtic were
playing, I was surprised to see some fans waving an alternative version of the
Irish Tricolour. This left off the orange band and substituted a yellow one. I
speculate that this was done by fans who were unwilling to tolerate the
appearance of any Protestant symbol on their flag - even if it was that of the
Irish Republic itself. They would have known that yellow and white were the
colours of the Papacy and so substituted yellow. I have not seen any such flag
in recent years. I wonder how common it was 50 years ago?Kenneth Fraser,
18 November 2011